The present invention concerns a pneumatic apparatus for producing a spun yarn or thread from a fibre array using a vortex flow. From DE 41 05 108 (called DE""108 in the following) a pneumatic spinning device is known for producing a yarn or thread from a short fibre sliver. In a nozzle block presenting a hollow room with a conical support member, the fibres are subject to a rotating air stream and thus are caused to rotate in such a manner that they form a yarn or thread. The yarn is taken off via a spindle duct. At the base of the conical support member a fibre guide duct merges into the nozzle room from the exterior. This fibre guide duct serves for feeding the fibres, or the fibre sliver respectively, from the exterior into the hollow room. A needle-shaped guide element protrudes over the free end of the conical support member, the needle point being oriented towards the centre of the spindle duct of the spindle, which is arranged rotating or stationary. This device presents the disadvantage that the quality of the yarn produced cannot readily be influenced. Due to the layout, in particular of the fibre guide duct, the twist imparted to the fibres by the rotating air stream tends to propagate right into the guide duct. Due to abrupt transitions, particularly between the fibre guide duct and the nozzle room, vortices and turbulences are generated, which exert negative influences. This is a substantial disadvantage. The yarn quality in this arrangement thus does not remain constant, but fluctuates.
From DE 40 36 119 (called DE""119 in the following) a further pneumatic spinning device is known serving for producing a yarn or thread from short fibers. This device also comprises a nozzle block. In its inside, however, as different from the arrangement described in DE""108, no conical support member is provided. Instead of the support member this device comprises a guide element substantially consisting of a wire pointed towards an opening of a rotating or stationary spindle. The function of this arrangement otherwise to a large extent is analogous to the one shown in the DE""108 and thus not discussed in more detail here. This device shows the disadvantage, in particular, that yarn quality substantially cannot be controlled. Because of the uncontrolled airflow supplied into the hollow room and to the zone, to which the fibre sliver is supplied, control of yarn quality is very difficult to achieve.
The arrangements known according to the state of the art are laid out in the zone in which the fibre sliver is fed into the nozzle block, and in the zone in which the fibres are exposed to the rotating air flow, which among other points favours uncontrolled air flows. Turbulences and fluctuating airflows negatively affect the yarn quality and limit the processing speed. The rotational movement generated by the air stream acting onto the fibres furthermore can be controlled with difficulties only and acts rights into the fibre guide duct.
It is thus a principal objective of the present invention laid open here, to develop the arrangements known according to the state of the art in such a manner that an improved and constant yarn quality is achieved. In particular yarn quality is to be rendered settable and controllable specifically. Additional objects and advantages of the invention will be set forth in the following description, or may be obvious from the description, or may be learned through practice of the invention.
The present invention laid open here shows a pneumatic spinning apparatus for producing a yarn spun from staple fibres. A nozzle block internally contains a hollow room with jet nozzles. In this hollow room a guide means is arranged coaxially opposite a substantially cylindrical spindle, which guide means merges into a fibre guide duct, or comes from it respectively. The fibre guide duct merges into the hollow room from the exterior and serves for feeding fibres, or a fibre sliver respectively, e.g. from a supply device. The layout and the arrangement of the fibre guide duct and of the fibre guide means is of considerable importance for the yarn characteristics and the resulting yarn quality. The fibre feed duct advantageously is laid out under consideration of aerodynamic aspects.
The spindle arranged opposite the fibre guide means is stationary or rotatable and comprises a spindle duct extending substantially centric, which serves for taking off the yarn spun. The fibre guide duct advantageously is arranged laterally offset with respect to the spindle. During processing the fibre sliver supplied by a supply device is brought into the hollow room via the fibre guide duct. In close vicinity of the merging point of the spindle duct the fibres are exposed to a spiraling rotating air stream, which is generated by the jet nozzles arranged substantially tangentially with respect to the spindle and the fibre guide means. In this process the fibres around the fibre guide means are exposed directly to the rotating air stream, which exerts a separating force away from the fibre sliver, acting onto fibre ends not guided in the fibre guide duct. The arrangement of the spindle, of the fibre guide means, and of the fibre guide duct are chosen in such a manner that the leading fibre end (fibre end zone entering the opening of the spindle duct first) of the fibres already forms a yarn while the trailing fibre end (fibre end zone entering the opening of the spindle duct not first) of the fibres is lifted off by the force acting towards the outside. This trailing free end of the fibres is arranged spiraling and rotating about the spindle. In the further course of the fibre sliver processing the fibres gradually are taken in into the spindle duct where they wrap around the fibre guide means in such a manner that a spun yarn with real twist results.
Owing to the fibre guide means and the fibre guide duct laid out and arranged according to the present invention, the fibres of the fibre sliver supplied via the fibre guide duct hardly can wrap around each other in uncontrolled manner. The fibre guide means furthermore functions as a so-called false core, which together with the fibre guide duct laid out and arranged to the present invention controls the propagation of the twist during the yarn formation. In this manner false twisting of fibres is prevented, or that a false twist propagating from the fibre guide means back towards the fibre guide duct in the direction towards the delivery device respectively, which would prevent imparting of real twist at least partially, and would affect yarn quality.
The fibre guide duct and the fibre guide means preferentially are formed continuously and aerodynamically shaped, and depending on the effect to be achieved, are laid out symmetrically or asymmetrically, tapered or bulbous. Other shapes and arrangements of the fibre guide means are possible also.
The layout and the arrangement of the fibre guide duct, via which the fibre sliver or the fibres are fed from the delivery device into the hollow room in the nozzle block, exerts considerable influence onto the processing and onto the resulting yarn. In the fibre guide duct the fibres of the fibre sliver are prepared for the spinning process, being oriented and arranged before they enter the hollow room, and before they are exposed to the rotating air stream. The layout and the cross-section profile along the fibre feed duct determine the manner in which the fibre sliver and the fibres are transformed and prepared. The duct is laid out in such a manner that a controlled air stream, directed from the outside into the nozzle block, prevails inside the duct, and influences the orientation and the arrangement of the fibres. Depending on the layout of the cross-section over the duct length it can be achieved that e.g. the fibres are fed into the process in rather crimped form or in rather straightened form in such a manner that yarns of different characteristics can be produced. The form and the arrangement of the duct also influence the twist imparting process, and the fibre guidance, of the fibres in the spinning process. By specifically designing the fibre guide duct and the air stream conditions therein the constancy of the yarn quality is optimised.
The design of the duct cross-section influences the air stream conditions, the pressure distribution along the duct and the fibre distribution. By specifically guiding the air stream, and if required controlled vortex formation, undesirable twisting of the fibres, particularly in the fibre guide duct, is avoided. Advantageously the fibre guide duct is formed smoothly without abrupt changes in cross-section. Angles and edges, which cause negative air streams, particularly breakdown of the air stream and turbulences, are to be avoided. The fibre guide duct advantageously merges into the fibre guide means smoothly without abrupt transitions.
The fibre guide duct, if required, can be laid out, at least over portions of the length, with various cross-sections and can be provided with additional fibre guide means such as ribs, lamellae or recesses, which assist prevention of fibre twisting. The air stream in the fibre guide duct is controlled and guided, if required, using specific guide means e.g. in the form of lamellae or profiled elements influencing the airflow with the help of pressure differences.
The fibre guide duct along its length presents a variable duct cross-section. The duct is laid out in such a manner that the fibres to be processed are transformed in specific manner and prepared for the spinning process. The fibre guide duct preferentially presents, at least over portions of its lengths, an oval circular, semi-circular, circle-segment, kidney-shaped, heart-shaped, sickle shaped, or half-moon-shaped form, or along its length or in a cross-section presents a combination of these and other forms. Grooves or protrusions extending longitudinally and integrated in the cross-section also are suitable. Using such layouts air pressure and air speed distribution along the duct can be controlled locally. With the help of additional fluid sources or fluid drains, e.g. in the form of nozzles arranged merging into the fibre guide duct, the air stream is controlled specifically as required and the fibre transformation is influenced. The fibre guide duct along its length presents, depending on the requirements, a continuous form, at least over portions of its length, in such a manner that no negative turbulences and air stream breakdowns occur. The wall of the fibre guide duct preferentially merges smoothly into the fibre guide means without abrupt changes in direction. The fibre guide means advantageously extends right into the fibre guide duct or adjoins it.
The yarn formation is effected after the start of a spinning start-up process of any type desired, e.g. by inserting a yarn end of yarn already spun back through the spindle duct into the zone of the spindle intake mouth until fibres of this yarn end are opened by the already rotating air stream to such extent that fibre front ends freshly supplied can be grabbed by this rotating fibre array, and by then pulling back the yarn end inserted, can be held therein, in such a manner that the trailing ends of the freshly supplied fibres can wrap around the leading fibre ends already located in the mouth zone of the spindle duct, in which arrangement the above mentioned yarn with an essentially predetermined piecing can be produced again.